Railway track circuits



NOV. 9, 1937. H, G. WITMER 2,098,848

RAILWAY TRACK CIRCUITS Filed Feb. 2l, 1935 INVENTOR l Harold G. I/zfmen BY @2f/151ML@ H IS ATTORNEY Patented Nov. 9, 1937 UNITED STATES PATENT GFFICE RAILWAY TRACK CIRCUITS Harold G. Witmer, Pittsburgh, Pa., assigner to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application February 21, 1935, Serial No. 7,602

11 Claims. (Cl. 246-34) My invention relates in general to railway track Winding P2 of transformer T2, which induces just circuits; and more particularly to track circuits enough voltage in the described loop circuit to wherein a minimum reduction of current flow in break down the glow discharge tube GDT and the track circuit employed to pick up the track permit current to flow through it when the track 5 relay will be required to effect the release of the ballast leakage is greatest. The resulting current 5 track relay. ilow through the primary winding P3 of step- I am aware that various methods of increasing down transformer T3 induces a current flow in its the release sensitivity of a track circuit have heresecondary winding S3, Causing the traek relay TR tofore been proposed, but most of these with to be energized through the rectifier BR.

which I am familiar approach the problem by, in The character of the glow discharge tube GDT 10 one manner or another, changing the release seniS Sueh that the Voltage required tO break dOWn sitivity of the track relay itself, so that a less the tube is Very nearly the Same aS that at which effective shunt across the track rails will shunt the tube cuts off. Therefore, in response t0 a drop suincient current from the track relay to effect its in pOtential-Very Small COInpared t0 that rerelease than would otherwise be required. quired t0 drop a traCk relay directly energiZed 15 One of the main features of my invention has to OVer the track circuit by Shunting Current from do with the provision of means sensitive to a slight it-the tube Will Cut Off and CeaSe feeding Current reduction in current flow in that portion of the t0 the track relay. track circuit which feeds the track relay, to open The primary Winding P3 0f tranSfOrIner T3 may the circuit of the track relay, or in another manbe designed to have Sufficient impedance t0 prOp- 2o ner remove all operating current therefrom to erly limit the flOW 0f Current through the tube effect its re1easewhen the tube breaks down; and fuse F or a lamp I will describe various forms of the track circuit is employed as a moans for opening the tube cirembodying my inventiony and wi11 then point; out; cuit in case the elements of the tube become the novel features thereof in o1aim5 short-circuited due to physical breakage of the 25 In the accompanying drawing, Fig, 1 is a diatube. As most of the voltage drop is normally grammatic View 0f one form 0f apparatus emaClOSS the Elements Of the tube, lf these Elements bodyng my invention; While Figs, 2 6 are dashould become short-circuited, sufficient current grammatic View-S 0f other forms 0f apparatus, Will OW t0 blOW the USG OI' blllXl Out the lament each of Which also embodies my invention, Of the lamp, thus Opening the Circuit. 30

Similar reference characters refer to similar F01' the purposes 0f explaining the OperatiOn Of parts in each of the several views. the track CirCuit Of Fig. 1, I Will assume that the Referring to Fig. 1, the reference characters 4 tube GDT breaks dOWn 0n any potential Over 50 and 5 designato the rails of a section A B of rail- Volts, and will cut off on potentials under 50 volts.

Way track separated from adjoining sections by The tIaCk CIClllt Will accordingly be adjusted t0 35 insulators 6 in the usual manner, and over which feed Slightly mere than 50 VOltS t0 the SeCOndary traffic normally moves in the direction indicated S2 0f the transformer T2 and accordingly aCrOSS by the arrow the terminals of the tube GDT under greatest Alternating current is fed to the rails 4 and 5 of ballast leakage conditions. The tube then breaks the section, at the exit end thereof, from the secdOWn and enables the transformer T3 and recti- 40 ondary Sl of a suitable transformer Tl via, a, ourfier BR to deliver normal operating current to the rent limiting reactor 1. At the entrance end of track relay TR. the track section, the primary Winding P2 of a, When the track section becomes occupied any step-up transformer T2 is bridged aoross the shunt on the track which will reduce the potentrack rails 4 and 5. The secondary winding s2 of tial in the loop Circuit including the tube GDT 45' transformer T2 is included in a loop circuit inbelOW 50 VOltS, Say t0 49 VOltS, Will cause the tube cluding a fuse F, the primary winding P3 of a t0 autOmatiCally Cut Off the energy Supply t0 step-down transformer T3, and a Geissler or glow tranSfOrrner T3 and aCCOr'dingly t0 the track redischarge tube GDT of the type having two like lay, as the tube will not conduct current unless plain electrodes which allow passage of current the potential in its circuit is over 50 volts. The 50 in both directions. The secondary winding S3 of armature of the track relay will accordingly be transformer T3 is connected to the terminals of released as a result of the complete removal of the track relay TR, through a rectifier BR. operating current from its winding, rather than 'I'he current normally supplied to the rails 4 and as in the formerly referred to arrangements, 5 by transformer TI is received by the primary wherein release of the relay armature depends on 55 a reduction of current ow below that required to hold its armature in the operated position.

In Fig. 2, I have shown the track relay TR as an alternating current relay and therefore connected in series with the secondary of the transformer T2 and the tube GDT. With this arrangement, the operation will be essentially the same as that described for Fig. 1. Explaining the operation more specifically, a slight drop in potential across the terminals of the primary winding P2 of the transformer T2 will drop the potential across the secondary winding S2 of this transformer to a point sufficiently below the break down value of the tube GDT to cause it to cut oii. When the tube cuts off, the supply of operating current to the track relay is interrupted, causing it to immediately release its armature.

In Fig. 3, I have shown a track relay directly included in the secondary portion of thetrack circuit, as in Fig. 2, but instead of employing a glow discharge tube of the type having two like plain electrcdes,allowing passage of current in both directions, I have employed a glow discharge tube GDRT of the rec'tier type employing one plain and one point type of electrode, thereby enabling me to employ a direct current track relay instead of one of the alternating current type. The break down and cut oiT operating characteristics of the tube GDRT are the same as of the type employed in Figs. land 2.

In Fig. 4, I have shown the tube GDRT connected in multiple with the track relay. With the secondary portion ofthe track circuit arranged in this manner and with a normal current flow through the primary circuit, the tube breaks down and during alternate half-cycles of the alternating current, shunts current away `from th-e track relay, while during the remaining half-cycles the current will be flowing through the track relay, so that the relay is picked up and held up by those unidirectional pulses of current not shunted by the tube. The track relay is, in this form of the invention, necessarily so designed that it will not pick up nor be held up by unrecti- 'ed alternating current, so that when the tube cuts off in response to a reduction of the alternating current potential, the relay will promptly release its armature. I have shown a resistor 8 connected in series with the tube GDRT to limit the current flow through it when the tube breaks down. It will be understood, however, that, with any ofthe arrangements shown, the impedance of the rails, leakage between the rails, and the reactor 'l will tend to limit the ilow of current at such time.

In Fig. 5, I have shown an arrangement similar to that shown in Fig. 3 except that two rectifier type tubes GDRT are employed. It will be apparent that with this arrangement, when the tubes break down, they will function as aV full wave rectifier, and therefore current will flow Athrough the relay in the same direction for each half-cycle of the alternating current, and will cut off the current supply to the track relay when the tubes cut off in response to a reduction in `potential in its operating circuit.

It will be apparent that the results obtained r`in Figs. 3, 4 and 5, by employment of a glow discharge tube of the rectifier type, may also be ob- .tained by employing a glow discharge tube such Fig. 3, wherein a rectifier is connected in series with the glow discharge tube GDT.

In concluding the description of my invention,

I wish to emphasize that, since the tubes em-Y ployedby me are of a type which will not allow any current to pass until the voltage supplied to them has increased to their break down Value, after which the current is limited almost entirely by the impedance in series with the circuit, it is evident that in the various forms of my invention the pick-up and release values of the track relays will be practically the same. My invention, therefore, teaches various methods of providing a track circuit having greater sensitivity than can be obtained with a track circuit wherein a standard relay is directly included in the track circuit and has a release which depends on a reduction of the current Yiiow through it, rather than on a positive interruption of the current supplied thereto.

Y' Although I have shown herein only a limited number of variations of my invention, it will be apparent that variouschanges and modifications may be made therein within the scope of the appended yclaims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

l. In combination with a section of railway track, means supplying a potentialacross the rails of the section at one end thereof, a track relay and a transformer Vat the other end of the section, a bridge across the rails cfsaid section comprising the primary winding `of said transformer, and a glow discharge tube included in circuit with the secondary winding of said transformer responsive to pass operating current through the winding of the track relay when and only when the section is unoccupied and the potential of current supplied to the secondary winding of said transformer is above a predetermined minimum value whereby said track relay will release more positively due to the interruption, of the operating current when a train enters Ysaid section and the potential across said secondary winding decreases below said predetermined value.

2. In combination with a section `of railway track, means supplying a potential across the rails of the section at one end thereof, a track relay and a transformer at the other end of the section, a bridge across the. rails of lsaid section comprising the primary winding of said transformer, an operating circuit for said relay including the secondary winding of said transformer, and a device connected in said circuit having the characteristic of, opening and closing the circuit through itself in response to slight variations in potential in the operating circuit such as occur when a train enters and leaves the section, respectively, whereby the operating circuit for said track relay will be interrupted to insure the release of said track relay upon the entry of a-train into said section.

3. In combination with a section of railway G5 track, means supplying a potential across the rails of the section at one end thereof, ya track relay and a transformer at the other end of vthe section, a bridge vacross the l rails `of said section comprising the primary winding of said transg,

la vehicle enters the sectionyandmeans-included 575 in said operating circuit for passing operating current to said track relay when and only when the section is unoccupied and responsive to the decrease in potential when the section becomes occupied to entirely cut off the supply of current to said relay.

4. In combination with a section of railway track, means supplying a potential across the rails of the section at one end thereof, a track relay and a transformer at the other end of the section, a bridge across the rails of said section comprising the primary winding of said transformer, a circuit including a glow discharge tube and the secondary winding of said transformer for supplying operating current to said relay when and only when the section is unoccupied and for completely interrupting the current when the section becomes occupied, and means included in said circuit for preventing said relay receiving current from the secondary winding of said transformer should the elements of said tube become short circuited.

5. In combination with a section of railway track, a transformer having its primary winding connected in bridge of the rails of the section, a track relay for said section, a glow discharge tube connected in series with the secondary winding of said transformer in an otherwise closed circuit and effective when and only when a break down potential is received by the secondary winding of said transformer to pass operating current on to the track relay, and means for supplying the track rails of the section with a suitable potential for effecting the discharge or break down of said tube when said section is unoccupied, whereby said operating current will be completely interrupted when the section becomes occupied.

6. In combination with a section of railway track, means supplying a potential across the rails of the section at one end thereof, a track relay and a transformer at the other end of the section, a bridge across the rails of said section comprising the primary winding of said transformer, and an operating circuit for said relay including the secondary winding of said transformer and a glow discharge tube, the parts being so proportioned that when a train enters said section the glow discharge tube will cut-off and will interrupt said operating circuit to insure the release of said track relay.

7. In combination with a section of railway track, means supplying a potential across the rails of the section at one end thereof, a track relay and a transformer at the other end of the section, a bridge across the rails of said section comprising the primary winding of said transformer; a control circuit for said relay including the secondary winding of said transformer, the primary winding of a second transformer and a glow discharge tube; and an operating circuit for said relay including a rectifier receiving current from the secondary winding of said second transformer.

8. In combination with a section of railway track, means supplying a potential across the rails of the section at one end thereof, a track relay and a transformer at the other end of the section, a bridge across the rails of said section comprising the primary winding of said transformer; a circuit including the secondary Winding of said transformer receiving current supplied to the primary thereof and including a glow discharge tube through which current of the potential supplied to the rails of said section normally flows, and the primary Winding of a second transformer; a circuit including the secondary winding of the second transformer and the input side of a rectifier, and a track relay operated from current supplied by the rectifier so long as the potential across the secondary winding of the first transformer is sufficient to prevent the cut oi of said glow discharge tube.

9. In combination with a section of railway track, means supplying a given potential across the rails of the section at one end thereof, a track relay and a transformer at the other end of the section, a bridge across the rails of said section comprising the primary winding of said transformer, and an operating circuit for said relay comprising the secondary winding of said transformer shunted by a glow discharge tube of the rectifier type.

10. In combination with a section of railway track, means supplying a given potential across the rails of the section at one end thereof, a track relay and a transformer at the other end of the section, a bridge across the rails of said section comprising the primary winding of said transformer, and an operating circuit for said track relay alternately including one and then the other of two glow discharge tubes connected in series with opposite halves of the secondary winding of said transformer.

11. In combination with a section of railway track, means supplying a potential across the rails of the section at one part thereof, a track relay and an inductive coupling, a bridge across the rails at another part of said section cornprising one portion of said inductive coupling,

and means including a glow discharge tube and the other portion of said inductive coupling connected in series for supplying operating current to said relay, the parts being so proportioned that when a train enters said section the glow discharge tube will cut-off and will interrupt the operating current to insure the release of said track relay.

HAROLD G. WITMER. 

